Generally, batteries are used to supply power to portable devices such as personal computers, radios, radiophones, stereo cassette tape players etc. Such batteries are typically available in two different types such as those characterized as rechargeable or non-rechargeable and exhibit different end-of-life voltage characteristics and effective series resistances. Non-rechargeable battery types are those ordinary alkaline batteries that should not be subjected to recharging attempts. Rechargeable battery types include nickel-cadmium (Ni—Cd), nickel-hydrogen (Ni—H), lithium-ion (Li-Ion), and nickel metal-hydride (Ni—MH). Also, a Constant Current-Constant Voltage (CC-CV) charging algorithm is common for most modern rechargeable batteries.
Typically, for a Li-Ion battery, battery charging is performed as follows. The supply voltage VDD is regulated to a fixed voltage throughout the battery charging. If the battery voltage is below a minimum safe operating voltage (e.g. 3.0V), the charge current is regulated to a constant current corresponding to 0.1 C, which is referred to as “pre-charge mode”. C represents battery capacity, typically measured in milliAmpere-hours (mA*hr). So, for a battery with a capacity of 1000 mA*hr, if the battery voltage is below the minimum safe operating voltage (e.g. 3.0V), then the charge current is regulated to 100 mA. Once the battery voltage reaches the minimum safe operating voltage, the charge current is regulated at a constant current corresponding to 1 C (e.g. 1 A, for a 1000 mA*hr battery). The battery charger remains in constant current (CC) mode, regulating the charge current to a constant current, until the battery voltage reaches the maximum safe operating voltage (e.g. 4.2V). At this point, the battery charger enters a constant voltage (CV) mode, where the battery voltage remains at 4.2V until the battery is fully charged.